Current semiconductor industry trends indicate that the development of high performance logic processors and 1-Gbit DRAM will require the availability of below 0.18 .mu.m lithographic processes. In theory, two methods of forming finer resist patterns are to shorten the wavelength of an exposure light source and increase the numerical aperture (NA) of an exposure system.
Semiconductor industry implemented in manufacture of devices by deep UV lithography employing a KrF excimer laser (248 .mu.m) stepper for 0.25 .mu.m process. Due to the optical enhancement techniques such as high NA optical elements, phase shift mask, etc. The appearance of 248 .mu.m KrF scanner offers the pilot-run of 0.18 .mu.m process and development of below 0.15 .mu.m process. However, there is a limit of wavelength shorten, the more difficult of mask produced. In order to minimize the device size, efforts to develop 193 .mu.m (ArF excimer laser) lithography and resists have been tremendously accelerated in the last several years.
In addition to improved resolution, it is also desirable to provide positive resist materials having improved sensitivity. One approach to improving sensitivity uses the concept of chemical amplification. Chemical amplification involves the photogeneration within the resists of species that catalyze subsequent chemical events. One method of chemical amplification includes dissolution inhibition, wherein a masked phenol or protected carboxylic acid is mixed with a phenolic resin, resulting in a drastic decrease in the dissolution rate of the polymer in aqueous base developing solutions. A photoactivated acid-catalyzed deprotection reaction is then used to free the phenol or the carboxylic acid. As a result, the dissolution inhibitor is converted into a dissolution promoter in the radiation exposed areas of the resist material, allowing for the development of positive images.
There remains a need in the art for a positive photoresist composition having both high resolution and high sensitivity. There also remains a need in the art of composition for positive photoresist, which are useful in deep-UV image resolution techniques. Moreover, there remains a need in the art for positive photoresist dissolution inhibitors capable of providing high sensitivity.